Molecular Modeling of PMR-15 Polyimide

PMR-15 polyimide is a polymer that is used as a matrix in composites. These composites with PMR-15 matrices are called advanced polymer matrix composite that is abundantly used in the aerospace and electronics industries because of its high temperature resistivity. Apart from having high temperature sustainability, PMR-15 composites also display good thermal-oxidative stability, mechanical properties, processability and low costs, which makes it a suitable material for manufacturing aircraft structures. PMR-15 uses the reverse Diels-Alder (RDA) method for crosslinking which provides it with the groundwork for its distinctive thermal stability and a range of 280-300 degree Centigrade use temperature. Regardless of such desirable properties, this material has a number of limitations that compromises its application on a large scale basis. PMR-15 composites has been known to be very vulnerable to micro-cracking at inter and intra-laminar cracking. But the major factor that hinders its demand is PMR-15\u27s carcinogenic constituent, methylene dianilineme (MDA), also a liver toxin. The necessity of providing a safe working environment during its production adds up to the cost of this material. In this study, Molecular Dynamics and Energy Minimization techniques are utilized to simulate a structure of PMR-15 at a given density of 1.324 g/cc and an attempt to recreate the polyimide to reduce the number of experimental testing and hence subdue the health hazards as well as the cost involved in its production. Even though this study does not involve in validating any mechanical properties of the model, it could be used in future for the validation of its properties and further testing for different properties like aging, microcracking, creep etc

Precise Asymptotics in Wichura's Law of Iterated Logarithm

Let {Xn, n ≥ 1} be a sequence of independent and identically distributed random variables with a common distribution function F = P(X ≤ x) in the domain of attraction of an asymmetric stable law, with index α, 1 < α < 2 and set Sn=∑nK=1XK. We prove                                         limε->0(√ε) ∑n≥3(1/n)P(Sn≤(θα-ε)An )=1/(2√2α), where An = n1/α(log log n)((α-1)/α) θα =(B(α))((α-1)/α) and B(α) = (1 − α)α(α/(1-α)) (cos (πα/2)) (α/α-1

Prevalence of Hypertension and Assessment of "Rule of Halves" in Rural Population of Basavanapura Village, Nanjangud Taluk, South India

Context: World Health Day is celebrated on 7 th April to mark the anniversary of the founding of World Health Organization in 1948. Each year a theme is selected for World Health Day that highlights a priority area of public health concern in the world. The theme for 2013 is on high blood pressure (BP). High BP, if left uncontrolled increases the risk of heart attacks, strokes, and kidney failure. Materials and Methods: A community-based cross-sectional survey was carried out among adults (>18 years) in Basavanapura Village, Nanjangud Taluk using simple random sampling method to study the pattern of BP using the Seventh Report of the Joint National Committee criteria. A total of 447 persons were screened. A total of 223 individuals (90 men and 133 women) were selected by simple random sampling, interviewed, and clinically examined for hypertension. BP of all the study participants was measured using a standardized technique. Statistical Analysis Used: Mean ± standard deviation (continuous data), proportions and percentages (categorical data), Chi-square test (association between age and hypertension) and odds were calculated to see in which age group the risk of hypertension was more. Kruskal-Wallis test was used to test the significant difference of systolic BP and diastolic BP for males and females among age groups. Results: Of the 447 persons surveyed in Basavanpura Village, BP was recorded among 223 individuals. The overall prevalence of hypertension was found to be 36 (16.1%), of which 22 (61.1%) were diagnosed, 20 (90.90%) treated, and only 14 (70.0%) controlled. Increasing age, sedentary lifestyles, and male sex were identified as the predisposing factors. Conclusions: The prevalence of hypertension in the village is slightly higher (16.14%) than the national prevalence (14%). There is an urgent need to educate the people to modify the lifestyle and to monitor their BP values regularly